Process for the methylation of phenolic compounds

ABSTRACT

Phenolic compounds are methylated with methane in the presence of a metallic catalyst selected from nickel or cobalt or mixtures thereof at a temperature in the range of about 300° C. to around 475° C.

BACKGROUND OF THE INVENTION

This invention is directed to a process for methylating phenolic compounds having at least one replaceable hydrogen on the aromatic ring. More particularly, this invention is directed to a process for methylating phenol with methane.

Recently, several different methods have been proposed for methylating phenols. Methylated phenols include: cresols, xylenols and higher methylated phenols like di- and tri-methylphenol.

One such method is taught in an article entitled, "Alkylation of Phenol with Methane Over Solid Acids and Bases," by Tadao Nishizaki and Kozo Tanabe in Chemistry Letters, Pages 149-150, No. 2, February 1973, which is published by the Chemical Society of Japan. This method involves the alkylation of phenol with methane over silica-alumina; or alumina catalyst. The alkylation is conducted at a temperature in the range of 400°-500° C. and at atmospheric pressure. This article also teaches that catalysts such as silica-titania, magnesia-alumina, and magnesium oxide are catalytically inactive in the alkylation of phenol with methane.

Another methylation process is taught in U.S. Pat. No. 3,718,704 (Chapman, et al.). This process for methylating an organic compound, e.g., an aromatic compound with an hydroxy group, includes contacting the methylatable compound with carbon oxide containing reactant gas in the presence of an oxide of Group IB, IIB, and/or VIB metal containing catalyst at a temperature between 400° F. (204° C.) and about 1200° F. (649° C.). This patent also teaches that no appreciable methylated products were obtained when the conditions of the patent were employed, but catalysts were used that were different from those previously stated, for example, various supported catalysts like Group VIII metal oxides.

U.S. Pat. No. 3,822,271 (Lapporte) teaches another methylation process. This process involves methylating alkyl substituted benzenes, aniline, pyridine, and alkyl substituted aniline and pyridine compounds by a mixture of carbon dioxide and hydrogen in the presence of a Fischer Tropsch catalyst like hydrogen reduced oxides or borides of cobalt and/or nickel. The methylation is conducted at a temperature in the range of 150°-450° C. and at a pressure of 1.7-70 atmospheres.

Other methylation processes known in the art prepare ortho-methylphenols by reacting a phenol at a temperature in the range of 300° C.-450° C. with methanol in the presence of ferrite catalysts which contain a divalent metal selected from zinc, magnesium, cobalt, nickel, chromium or cadmium or a catlyst which is a sintered methane-containing of ferric oxide and at least one of the aforementioned divalent metal oxides and a small amount of manganese oxide.

The process for methylating phenols described herein is believed patentable over the known prior art because the prior art does not teach or suggest to one skilled in the art, and actually teaches away from, a method for methylating phenolic compounds with methane in the presence of specific metallic catatlysts.

SUMMARY OF THE INVENTION

Somewhat surprisingly, I have found that contrary to the teachings of the prior art, phenolic compounds can be methylated with methane in the presence of metallic catalysts selected from nickel or cobalt or mixtures compound thereof. The process of methylating the phenolic compound involves reacting the phenolic compound with a methane-containing gas in the presence of a metallic catalyst selected from nickel, cobalt or mixtures thereof at a temperature in the range of about 300° C. to around 475° C.

The term "phenolic compounds" includes, generally, a phenol with at least one replaceable hydrogen on the aromatic ring. Examples of these compounds include: phenol (monohydroxybenzene); alkylated phenols, for example, cresol and ethyl phenols; xylenols, and resorcinol, hydroquinone, catechol and their methylated and ethylated derivatives. The term "methane-containing gas" includes a gas which contains a substantial amount of methane, around at least fifty percent (50%) by weight, and may contain lesser amounts of inert gases such as nitrogen. Generally, the molar ratio of phenolic compounds to methane is in the range of about 0.5:1 to around 5:1. Although molar ratios outside this range could be used, such use would be uneconomical.

The methylation process of this invention is usually conducted at atmospheric pressure, but it may be conducted at super-atmospheric or sub-atomspheric pressures with a concomitant adjustment in the temperatures. The metallic catalyst is generally used in an amount to provide good contact times for the reactant. The metallic catalyst may be used alone or on an inert support such as kieselguhr, magnesia, silica, thoria, zirconia, titania, alumina, charcoal, and the like. In addition to the metallic catalyst being nickel or cobalt, the catalyst may consist of a mixture of nickel and cobalt in any proportions and with or without an inert support. The metallic catalyst may also contain a minor amount of the oxide of the nickel or cobalt metal present in the metallic catalysts. The metallic catalysts used in the methylation process of this invention may be made in any manner known to those skilled in the art.

The process of this invention yields ortho-, meta-, and para-cresol with lesser amounts of higher methylated phenols when the starting phenolic compound is phenol. When the starting phenolic compound is an alkylated phenol with at least one replaceable hydrogen atom on the aromatic ring, the process of this invention yields higher methylated phenols. The yields of methylated phenolic compounds obtained with the use of a metallic catalyst selected from nickel, cobalt or mixtures thereof are generally better than yields obtained with the use of alumina or silica-alumina catalysts.

DETAILED DESCRIPTION OF THE INVENTION

The methylation process of this invention is conducted under certain general conditions of temperature, equipment, manner of operation and contact time, but there are optimum conditions at which this process can be conducted depending upon the particular metallic catalyst used. The optimum conditions for a particular metallic catalyst may vary from other optimum conditions for other particular metallic catalysts; but all of the optimum conditions will still be within the generally specified conditions.

Generally, the methylation process of this invention can be performed in any reactor known by those skilled in the art to be used for vapor phase catalytic reactions. Examples of these reactors are: fixed bed reactors, jiggling bed reactors, moving bed reactors or fluidized bed reactors. The methylation process of this invention may be performed in either a batch or continuous manner.

It is preferred to conduct the methylation process of this invention in a fixed bed reactor and in a continuous manner. This equipment and manner of operation allows for the production of methylated phenolic compounds in a facile and economic manner. The preferred phenolic compound which is methylated by the process of this invention is phenol since this compound is easily available and its methylated products, namely, mostly ortho-cresol, along with meta-cresol and para-cresol and a minor amount of higher methylated products are in demand for various end uses. The preferred methane-containing gas used to methylate the phenol is methane in the form of natural gas. Natural gas is the most readily available form of a methane-consisting gas. Several metallic catalysts selected from the group of nickel, cobalt, and mixtures thereof are preferred for methylating phenol with methane. These catalysts include: nickel catalyst No. 0104 manufactured by Harshaw Chemical Co., Cleveland, Ohio; nickel catalyst No. G-65 manufactured by Girdler Catalyst Department, Chemetron Chemicals Division, Chemetron Corp., Louisville, KY; nickel catalyst Houdralite 715X2-4 manufactured by Houdry Process Corp., Philadelphia, Pa.; and cobalt catalyst No. 0101 manufactured by Harshaw Chemical Co. These catalysts are preferred since they are commercially available metallic catalysts or metallic oxide catalysts which can be reduced.

The preferred embodiment for the methylation of phenolic compounds involves preparing a fixed bed reactor containing Harshaw nickel catalyst No. 0104 in an amount sufficient to allow for adequate contact time of the reactants with the catalyst. This nickel catalyst has a 58 percent total nickel content on kieselguhr wherein the ratio of nickel oxide to total nickel is 0.6-0.65:1 with a surface area of 155 to 165 square meters per gram. The fixed bed is heated to a temperature in the range of 300° C. to about 475° C., and when the fixed bed reaches this temperature phenol and methane are separately introduced into the fixed bed catalyst reactor. To facilitate handling, it is preferred to add the phenol as a liquid to the top of the fixed bed catalyst reactor. Methane is introduced into the fixed bed catalyst reactor as a gas. Both phenol and methane pass through the fixed bed catalyst reactor in a space velocity in the range of about 0.5 to around 10 LHSV and GHSV, respectively. Preferably the introduction of phenol into the fixed bed catalyst reactor is around 20 ml per hour and the methane is introduced into the fixed bed catalyst reactor at a rate of about 5.1 liters per hour for a single pass of the reactants over the fixed bed catalyst. In order to achieve the maximum yield of product and to avoid any complications due to catalyst fusion, the temperature of the fixed bed catalyst reactor is maintained preferably within the range of about 300° C. to around 430° C. The methylated phenols produced from the fixed bed catalyst reactor include predominantly ortho-cresol, and meta- and para-cresols with a minor amount of di-, tri- and tetra-methylated phenols; and minor amounts of aromatic hydrocarbons such as benzene and toluene due to the dehydroxylation of the phenol. To increase the yield of the methylated phenols from the fixed bed catalyst reactor, the methylated phenols produced in the first run can be recirculated to the fixed bed and passed through the bed several more times.

In an alternative embodiment of the methylation of phenol with methane, a fixed bed catalyst reactor is prepared with a hydrogenated Girdler nicke catalyst G-65. This catalyst is an oxidized nickel catalyst consisting of 25% nickel oxide deposited on a mixture of gamma and alpha alumina and having a surface area of 50 square meters per gram and a pore volume of 0.10 cubic centimeters per gram. Since this catalyst is an oxidized nickel catalyst, the catalyst must be reduced before catalyzing the reaction between phenol and methane. The Girdler nickel catalyst can be reduced at methylation temperatures by passing a stream of hydrogen through the catalyst bed for an average period of around 3 to 5 hours, although the time can be longer than 5 hours. After the Girdler catalyst has been reduced, phenol and methane are introduced separately into the fixed bed catalyst reactor. This introduction is performed in the same manner as in the first embodiment of this invention which was previously discussed. In order to obtain the maximum yield of methylated phenols in each run through the fixed bed catalyst reactor and to avoid the possibility of catalyst fusion, the temperature of the fixed bed catalyst reactor is maintained preferably within the range of about 375° C. to around 450° C. The methylated phenols produced from this fixed bed catalyst reactor contains predominantly ortho-cresol with smaller amounts of meta- and para-cresol and di-, tri- and tetra-phenols; and minor amounts of benzene and toluene which are due to the dehydroxylation of phenol and cresols, respectively. The yield of these methylated phenols may be increased by rerunning the product through the fixed bed catalyst reactor several more times.

In another alternative embodiment for methylating phenol with methane, the process is performed in a manner similar to the second above-described embodiment except that the Girdler nickel catalyst, G-65, is replaced with a Houndry nickel Houdralite catalyst, 715X2-4. This catalyst consists of 10% nickel oxide on a silica-alumina support and has a surface area of 400 square meters per gram and a porosity of 0.28 cubic centimeters per gram. As with the Girdler nickel catalyst G-65, the Houdralite nickel catalyst 715X2-4 is reduced with hydrogen for a period of about 3 to 5 hours before it is used to catalyze the methylation of phenol with methane.

In yet another alternative embodiment for methylating phenol with methane, a fixed bed catalyst reactor is prepared containing Harshaw cobalt catalyst CO-0101. This catalyst consists of 35% cobalt as cobalt oxide deposited on a kieselguhr support. As with the Girdler and Houdralite catalyst, this catalyst must be reduced by passing hydrogen through the fixed bed for a period of about 3 to 5 hours. Then, as in the above-described embodiments, phenol and methane are passed through the heated fixed bed reactor and a methylated phenol product is obtained which contains predominantly ortho-cresol with smaller amounts of meta- and para-cresol, and di-, tri- and tetra-phenols with smaller amounts of benzene and toluene. Again, to increase the yield of the methylated phenols the methylated phenolic effluent from the fixed bed catalyst reactor can be recycled and rerun through the fixed bed catalyst reactor several additional times. In order to maximize the yield of methylated products obtained from the fixed bed catalyst reactor for each run and to avoid any complication due to catalyst fusion, the temperature of the fixed bed catalyst reactor is maintained preferably within the range of about 380 to around 430° C.

An example of another metallic catalyst that can be used in the process of this invention is a reduced nickel oxide on a silica support. The nickel oxide on silica catalyst can be obtained by the designation T-1502A from Girdler Catalyst Department of Chemetron Chemicals Division, Chemetron Corporation.

After a period of time of catalyzing the reaction, the metallic catalyst may become deactivated because of a coating of carbon on the catalyst. The carbon coating has a tendency to deactivate the catalyst. The deactivated metallic catalyst may be reactivated in the fixed bed catalyst reactor after the reactor has shut down or in a separate stage of the fixed bed catalyst reactor or in a separate reactor. The separate reactor may be a fixed bed, moving bed or fluidized bed regenerator. The deactivated metallic catalyst is subjected to hot air and/or steam at a temperature of around 450° C. to burn the carbon coating from the deactivated catalyst. After the carbon coating is purged, the metallic catalyst then may have to be reactivated with hydrogen before it can again catalyze the methylation reaction.

In order to more fully illustrate the methylation process of this invention, reference is made to Table I. This table contains data for several experiments wherein phenol and methane were reacted in the presence of either Harshaw nickel catalyst NI-0104, reduced Girdler nickel catalyst G-65, reduced Houndry nickel catalyst Houdralite 715X2-4, or reduced Harshaw cobalt catalyst CO-0101. Table I also contains several experiments wherein phenol and methanol were reacted over a fixed bed catalyst of either alumina or silica-alumina. The data on these runs are included in Table I in order to show the unexpected results that the use of a metallic catalyst selected from the group of nickel, cobalt or mixtures thereof yield increased amounts of methylated phenols over the amount of methylated phenols obtained from an alumina-silica catalyst or an alumina catalyst.

                                      TABLE I                                      __________________________________________________________________________     METHYLATION OF PHENOL USING METHANE (1/1 mole ratio-single pass)                                     GC Analyses, Area Percent                                                                       Me.sub.2, Me.sub.3                                        Max.                 and                Phenyl               Expt.             Temp.                                                                              Phenol                                                                               o-Cresol                                                                            m,p-Cresols                                                                          Me.sub.4 Phenols                                                                      Benzene                                                                              Toluene                                                                              Ether                No. Catalyst      ° C.                                                                        min.-max.                                                                            min.-max.                                                                           min.-max.                                                                            min.-max.                                                                             min.-max.                                                                            min.-max.                                                                            min.-max.            __________________________________________________________________________      1  Nickel,       318 98.74-99.99                                                                          0.02-1.26                                              Ni-0104-Harshaw                                                             2  Nickel,       375 95.66-99.68                                                                          0.25-2.04         0.07-2.10                                                                              0-0.20                       Ni-0104-Harshaw                                                             3  Nickel,       383 81.40-89.15                                                                          2.56-5.65          6.20-11.78                                                                          0.38-0.81                      Ni-0104-Harshaw                                                             4  Reduced.sup.2 380 98.51-99.20                                                                          0.17-0.47         0.63-1.02                            Nickel Hydrogenation,                                                          G-65-Girdler                                                                5  Reduced.sup.2 440.sup.1                                                                          89.32-89.70                                                                          5.88-6.12                                                                           0.07-0.11                                                                            0.20-0.21                                                                             3.10-3.38                                                                            0.72-1.11                      Nickel Hydrogenation,                                                          G-65-Girdler                                                                6  Reduced.sup.2 386 99.49-99.84                                                                            0-0.14          0.16-0.37                            Nickel Oxide on Silica,                                                        T-1502A-Girdler                                                             7  Reduced.sup.2 425.sup.1                                                                          95.39-95.86                                                                          2.09-2.44                                                                             0-0.02                                                                               0-0.26                                                                              1.68-1.78                                                                            0.13-0.19                      Nickel Oxide on Silica,                                                        T-1502A-Girdler                                                             8  Reduced.sup.2 Nickel,                                                                        378 95.97-97.12                                                                          1.74-2.05         1.10-1.90                                                                            0.04-0.08                      Houdralite 715X2-4-Houdry                                                   9  Reduced.sup.2 Nickel,                                                                        444 86.54-89.91                                                                          5.16-7.48                                                                           0.51-0.62                                                                            0.60-0.97                                                                             2.76-2.85                                                                            0.77-1.30                                                                            0.17-0.23                Houdralite 715X2-4-Houdry                                                  10.sup.4                                                                           Reduced.sup.2 Cobalt,                                                                        380 93.00-97.23                                                                          0.76-2.63    0-0.56                                                                              1.94-2.95                                                                            0.07-0.73                                                                              0-0.07                 CO-0101-Harshaw                                                            11.sup.4                                                                           Reduced.sup.2 Cobalt,                                                                        423 43.59-74.59                                                                          4.95-7.41                                                                           0.68-0.70                                                                             3.13-20.09.sup.3                                                                      6.41-10.60                                                                           5.01-10.57                                                                          1.47-5.38            12  Activated     380 97.35-98.98                                                                          0.81-1.85                                                                           0.02-0.12                                                                            0.18-0.59                                                                             0.01-0.03   0.12-0.77                Gamma Alumina,                                                                 T-374-Girdler                                                              13  Activated     413 89.57-97.73                                                                          1.12-2.46                                                                           0.05-3.79                                                                            0.18-2.09                                                                             0.06-0.30                                                                              0-0.07                                                                               0-1.62                 Gamma Alumina,                                                                 T-374-Girdler                                                              14  Houdry 100S (Alumina)                                                                        373 97.09 14 98.74                                                                       1.26-2.91                                          15  Houdry 100S (Alumina)                                                                        409 96.68-99.78                                                                          0.11-1.06                                                                           0.11-1.01                                                                              0-0.89                                                                                 0-0.04     0-0.32             __________________________________________________________________________      .sup.1 High exotherm caused catalyst fusion at this temperature and            plugging resulted.                                                             .sup.2 H.sub.2 reduced for 3-5 hours prior to use.                             .sup.3 2,3,6-Trimethylphenol of 3.03-18.85% and tetramethylphenol of           0.10-1.24%.                                                                    .sup.4 Other components included Cyclohexanol and Anisole.               

According to the provisions of the Patent Statutes, the principle, preferred construction and mode of operation of the invention have been explained and what is considered to represent its best embodiment has been illustrated and described. However, it should be understood that within the scope of the appended claims, the inventions may be practiced otherwise than as specifically illustrated and described. 

I claim:
 1. A process for methylating mononuclear phenolic compounds, comprising:(a) reacting a mononuclear phonolic compound selected from the group consisting of phenol, phenols substituted with one to four primary alkyls each of one to six carbon atoms, phenols substituted with one to four secondary alkyls each of one to six carbon atoms, resorcinol, hydroquinone, catechol, and the methylated and ethylated derivatives of one to three primary or secondary alkyl group substituted resorcinol, hydroquinone and catechol with a methane-containing gas in the presence of a metallic catalyst selected from the group consisting of nickel, cobalt, and mixtures thereof at a temperature in the range of about 300° C. to about 475° C. to produce methylated mononuclear phenolic compounds.
 2. Process according to claim 1 wherein the mononuclear phenolic compound is phenol and the methane-containing gas is natural gas and the methylated mononuclear phenolic compounds are mainly ortho-cresol in a predominant amount and lesser amounts of meta- and para-cresol and di-, tri- and tetra-methylated phenols.
 3. Process according to claim 1 wherein the mononuclear phenolic compound and methane-containing gas are reacted at atmospheric pressure.
 4. Process according to claim 1 wherein the metallic catalyst selected from the group consisting of nickel, cobalt and mixtures thereof are supported on inert supports selected from the group consisting of kieselguhr, magnesia, silica, thoria, zirconia, titania, alumina, and charcoal.
 5. Process according to claim 1 wherein the metallic catalyst is a nickel oxide deposited on gamma and alpha alumina and which is subjected to reduction by passing hydrogen over the catalyst for a period of about 3-5 hours and which is used to catalyze the reaction between mononuclear phenolic compounds and a methane-contanining gas at a temperature of about 300° C. to around 450° C.
 6. Process according to claim 1 wherein the metallic catalyst is a cobalt oxide deposited on kieselguhr which is subjected to reduction by passing hydrogen over the catalyst for a period of about 3-5 hours and which is used to catalyze the reaction between the mononuclear phenolic compound and methane-containing gas at a temperature in the range of about 375° C. to around 430° C.
 7. Process according to claim 1 wherein the metallic catalyst has 58 percent total nickel content on kieselguhr wherein the ratio of nickel oxide to nickel is 0.6/0.65 which is used to catalyze the reaction between the mononuclear phenolic compounds and methane-containing gas at a temperature in the range of about 300° C. to around 430° C.
 8. Process according to claim 1 wherein the metallic catalyst is a nickel oxide deposited on a silica-alumina support which is subjected to reduction by passing hydrogen over the catalyst for a period of about 3 to around 5 hours.
 9. Process according to claim 1 wherein the catalyst is in a fixed bed reactor. 